During interval training, which energy system is primarily utilized?

• A. Phosphagen system
• B. Glycolytic metabolism
• C. Oxidative phosphorylation
• D. Lipid oxidation

Answer: (B)

During interval training the body works at high intensity for a short to moderate duration, so energy has to be produced quickly. The phosphagen system can provide ATP very fast, but it is exhausted within roughly 5–10 seconds. As work bouts extend beyond that, anaerobic glycolysis becomes the main source of ATP, supplying energy rapidly without needing oxygen. This glycolytic pathway is well-suited to the typical interval lengths (often tens of seconds to a couple of minutes) where the demand outpaces the slower aerobic system but the immediate phosphagen supply is largely depleted. Oxidative phosphorylation handles longer, lower-intensity efforts and recovers between bouts, while lipid oxidation is more characteristic of very low-intensity, longer-duration work. So, the primary energy system for interval training is glycolytic metabolism.